View Compilation Error

0_0_21886074_29416.cpp: In function 'void createTrie(char*)':
0_0_21886074_29416.cpp:10:23: error: 'strlen' was not declared in this scope
     int len=strlen(str);  
                       ^
0_0_21886074_29416.cpp: In function 'int findTrie(char*)':
0_0_21886074_29416.cpp:30:23: error: 'strlen' was not declared in this scope
     int len=strlen(str);  
                       ^